1. Field of the Invention
The instant disclosure relates to a door detection system, and more particularly, to a door detection system for judging whether a door of a wafer carrier device is closed or not.
2. Description of Related Art
In semiconductor manufacturing, lots of wafers have to be subjected to a fabrication process with multiple steps so as to be manufactured into desired semiconductor devices. In order to obtain profit, all the semiconductor manufacturers wish to reduce the time required for manufacturing lots of wafers, thereby increasing the yield of the semiconductor fabrication plant. There are many factors to influence the time required for manufacturing the wafers. In addition to the time required for manufacturing wafers on the respective fabrication machine tools, the time for transporting the wafers among different fabrication machine tools is also another critical factor. Hence, a common automatic transport system includes a plurality of overhead transport rail is created.
For example, a plurality of sets of fabrication machine tools is provided below each of the overhead transport rail sets. Each of the overhead transport rail sets defines a bay. The fabrication machine tools disposed in the same bay will be closely related to each other. The transport rail sets are provided with a plurality of overhead hoist transport vehicles (OHT vehicles) or called “vehicles” for short. The vehicles move on the overhead transport rail sets, whereby the wafer carrier can be transported from one fabrication machine tool to another fabrication machine tool. Further, each of the overhead transport rail sets is connected with another overhead transport rail set, so that the vehicles can move into different overhead transport rail sets to thereby transport the wafer carrier into the fabrication machine tool of another bay.
However, there is no door detection system known in the prior art automatic transport systems for determining whether the door of the wafer carrier is closed.